(a) Field of the Invention
Embodiments relates to a solar cell.
(b) Description of the Related Art
Recently, as existing energy sources, such as petroleum and coal, are expected to be depleted, interests in alternative energy sources for replacing the existing energy sources are increasing. Among the alternative energy sources, solar cells have been particularly spotlighted because, as cells for generating electric energy from solar energy, the solar cells are able to draw energy from an abundant source and do not cause environmental pollution.
A general solar cell includes a substrate and an emitter layer, formed of a semiconductor, each having a different conductive type, such as a p-type and an n-type, and electrodes respectively formed on the substrate and the emitter layer. The general solar cell also includes a p-n junction formed at an interface between the substrate and the emitter layer.
When light is incident on the solar cell, a plurality of electron-hole pairs are generated in the semiconductor. Each of the electron-hole pairs is separated into electrons and holes by the photovoltaic effect. Thus, the separated electrons move to the n-type semiconductor (e.g., the emitter layer) and the separated holes move to the p-type semiconductor (e.g., the substrate), and then the electrons and holes are collected by the electrodes electrically connected to the emitter layer and the substrate, respectively. The electrodes are connected to each other using electric wires to thereby obtain an electric power.
At least one current collector is positioned on each of the emitter layer and the substrate, and the current collector on the emitter layer and the current collector on the substrate are electrically connected to the corresponding electrodes, respectively. Hence, charges collected by the electrodes move to a load connected to the outside through the current collector adjacent to the electrodes.
However, in this case, because the current collectors are respectively formed on one surface of the substrate on which the light is not incident and the other surface of the substrate on which the light is incident (i.e., the emitter layer on an incident surface of the substrate), an incident area of the light is reduced. Hence, the efficiency of the solar cell is reduced.
Accordingly, a metal wrap through (MWT) solar cell and a back contact solar cell, etc., have been developed so as to decrease or prevent a reduction in the efficiency of the solar cell resulting from the current collectors blocking the light. In the MWT solar cell, a current collector connected to an emitter layer is positioned on a rear surface of a substrate opposite an incident surface of the substrate, and in the back contact solar cell, the electrodes collecting the electrons and the holes are positioned on the rear surface of the substrate.